MEMS Piezoresistive Pressure Sensor: a Survey

Shwetha Meti et.al. Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 4, (Part - 1) April 2016, pp.23-31 RESEARCH ARTICLE OPEN ACCESS

MEMS Piezoresistive Pressure Sensor: A Survey

Shwetha Meti*, Kirankumar B. Balavald*, B. G. Sheeparmatti* *(Department of Electronics and Communication, Basaveshwar Engineering College, Bagalkot-587102

ABSTRACT Piezoresistive pressure sensors are one of the very first products of MEMS technology, and are used in various fields like automotive industries, aerospace, biomedical applications, and household appliances. Amongst various transduction principles of pressure sensor piezoresistive transduction mechanism is widely used. Over a decade therehas been tremendous improvement in the development of the design of piezoresistive pressure sensor starting with the invention of piezoresistance in the silicon to the recent piezoresistive pressure sensor materials. Because of its high sensitivity, high gauge factor, independent to the temperature, linear operation over a wide range of pressure, and many more advantages. This paper provides survey of piezoresistive pressure sensor including their pressure sensing mechanism, evolution, materials, design considerations, performance parameter that to be considered and the fabrication process used Keywords-MEMS, Pressure sensor, Piezoresistor, Silicon material. Common methods that uses piezoresistive I. INTRODUCTION technologies are Silicon (Mono crystalline), In conjunction with temperature, pressure Polysilicon Thin Film, Bonded Metal Foil. 1.7 is one of the major physical quantities in our Capacitive pressure sensor uses a diaphragm and environment. A pressure sensor often acts as a pressure cavity to create a variable capacitor to transducer; it produces a signal as a function of the detect strain due to applied pressure, capacitance pressure imposed. MEMS pressure sensors are decreasing as pressure deforms the diaphragm. covering foremost part of the sensor market in 1.8Resonant pressure sensor uses the changes contemporary years and are fast developing with in resonant frequency in a sensing mechanism to brand new capabilities. Pressure sensors are used in measure stress, or changes in gas density, caused many applications like aerodynamics, biophysics, by applied pressure. automobile, safeguards and many more domestic Many MEMS instruments were applications. Various types of pressure sensors can manufactured and commercialized from several be categorized based on the sensing mechanisms years and have reached consumer. The present they are. 1.1 Absolute pressure sensor measures pressure sensors going through many challenges static, dynamic or whole pressure with reference to that has to be used in the application like high a vacuum. 1.2 Gauge pressure sensor calculates the pressure. Temperature is a main factor in the pressure relative to atmospheric pressure. When it efficiency of MEMS pressure sensor, were these shows zero, then the pressure it is measuring is have to be used in many applications like aerospace same as the ambient pressure. 1.3 Relative pressure utility and harsh environment. Consequently, for sensor measures static, dynamic or total pressure this kind of environment special sensing devices with regards to the ambient pressure. 1.4 Optical are requiring to adapt a high temperature and high pressure sensor techniques include the use of pressure environment. Among all the various type anphysical change in the optical fiber to detect the of MEMS pressure sensor piezoresistive pressure strain due to an applied pressure. This technology sensors are widely used, because these sensors is employed in many challenging applications provides a high sensitivity and it allows a linear where the measurement may be highly remote, operation over a wide range of pressure. under high temperature, or may benefit from Piezoresistive pressure sensors are one of the very applied sciences inherently immune to first products of MEMs technology. Those products electromagnetic interference. 1.5 Differential are broadly used in biomedical applications, pressure sensor measures the difference between automotive enterprises and household appliances. two pressures, one connected with each side of the The piezoresistive pressure sensor have mainly sensor. Differential pressure sensors are used to been studied and commercialized because of their measure many properties like pressure drops high yield and wide dynamic range. A silicon based through oil filters or air filters, fluid levels or flow pressure sensor is one of the major applications of rates. 1.6 Piezoresistive pressure sensor uses the piezoresistive sensor. Recently MEMS situated the piezoresistive effect of bonded strain gauges to technologies includes silicon (Si), silicon on detect the strain due to an applied pressure, insulator (SOI), silicon on sapphire (SOS), silicon resistance increasing as pressure deforms the carbide (SiC), steel, carbon nanotubes (CNT) and

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diamond had been observed to be in a position to doping concentrations are increased further [14, 15- furnish the critical ruggedness to be capable to 17]. Based on this phenomenon, the existing adapt and provide the better performance in harsh piezoresistive theories of Polysilicon were environment. This paper focus on the survey of established during 1980s~1990s and used to predict MEMS based piezoresistive pressure sensor, the process steps for the optimization of device current trends involved in development of performance. piezoresistive pressure sensor and their outlook. Later years carbon nanotubes have drawn Section II explains about the evolutions of much attention since their discovery in 1991 piezoresistive pressure sensor. Principle and because of their unique electronic and mechanical sensing mechanism of piezoresistive pressure properties. In 1991, multi-walled nanotubes were sensor is explained in section III. Section IV is first discovered by Ijima by arc-discharge about the materials that are used in the design of technique when he saw fine threads in a bit of shoot diaphragm and their properties. Section V and VI under electron microscope. The strands were very discuss about the performance parameter and the thin and long tubes of pure carbon. SWNTs were design consideration of the piezoresistive pressure synthesized for the first time by Ijima and Ichihashi sensor. The fabrication of the piezoresistive [18] and Bethune et al. [19] in 1993 using metal pressure sensor is discussed in section VII. catalyst in arc-discharge method. Laser-ablation technique was used by Thess et al. [20] in 1996 to II. EVALUTION OF PIEZORESISTIVE produce bundles of aligned SWNTs. For the first PRESSURE SENSOR time, catalytic growth of MWNTs by CVD was Ever since the discovery of proposed by Yacaman et al. [21]. Liu [22] and Dai Piezoresistance in silicon by C.S.Smith in1954 [1] [23] demonstrated that piezoresistive pressure silicon based micro pressure sensors have been sensors can be realized with CNTs. They grew extensively studied over the past three decades. SWNTs on suspended square polysilicon Pfann and Thurston [2] were among the first to membranes. When uniform air pressure was realize a working of MEMS based pressure sensor applied on the membranes, a change in resistance designed using two longitudinal and two transverse in the SWNTs was observed. Moreover, the diffused piezoresistors in the Whetstone's bridge membrane was restored to its original condition for better sensitivity. Kanda [3] in his work has when the gas was pumped out, indicating that the presented a model which enables the calculation of process is reversible. Dharap et al.[24] argued that piezoresistive coefficients as a function of doping the conventional sensors have disadvantage that concentration and temperature. Enhancing the they are discrete point, fixed directional, and are sensitivity has also been a main issue in the not embedded at the material level. To overcome research of micro pressure sensors. Design these limitations, they developed a CNT film modifications like employing a bossed diaphragm sensor for strain sensing on macro scale. The and multiple diaphragms [4, 5] and material sensor was based on the principle that the modification by using phosphorous diffused electronic properties of CNTs change when polysilicon piezoresistors [6] polymer diaphragms subjected to strains. In recent years high and alternate piezoresistive materials [7-10] have temperature pressure sensor is one of the hot also been studied. The other technology can be research topics in the industry. Because of the brought to solve the isolation problem of devices special environments they are used in, the and substrates, but increases the fabrication cost requirements for the design and manufacture of the greatly. The discovery of piezoresistive effect in sensor are very strict. It is important to research polysilicon in the 1970s [11] facilitates its high temperature pressure sensors for every walk of applications for sensing devices [12, 13]. As for life [25, 26]. So Silicon carbide (SiC) has been polysilicon, the p-n junction isolation is avoided, so recognized as an appropriatesemiconductor that the devices can work at higher temperatures. material for harsh environments such asspace Moreover, polysilicon based devices have the applications and terrestrial applications in the advantages of low cost, facile processing and good aeronautical,automotive and petrochemical fields thermal stability, compared to homogeneous silicon proposed Staufferet al; George et al. 2006 Many based devices. It can be seen that it is necessary to studies show thatSiC devices are capable of investigate the piezoresistive properties of operating well in these applicationsthat involve polysilicon and built up the theoretical model. The high-temperature, high-radiation andcorrosive experimental results reported by other researchers environment by Azevedo and Jones; indicated that the GF of Polysilicon common films WrightandHorsfall [27, 28] 2007. (PSCFs, film thickness ≥ 200 nm) reaches the Another material that can withstand the maximum as the doping concentration is at the high temperature and high pressure is a SOI. We level of 1019 cm3, and then decreases drastically as know that the temperature dependence of the

www.ijera.com 24|P a g e Shwetha Meti et.al. Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 4, (Part - 1) April 2016, pp.23-31 piezoresistive effect in silicon is well documented mechanical strain is applied [38]. In metals, this in the literature. It is known how the piezoresistive effect is realized when the change in geometry with coefficients change with the temperature. The applied mechanical strain results in a small increase temperature limit has been verified up to 175 °C for or decrease in the resistance of the metal. The silicon sensors and up to 500 °C for silicon-on- piezoresistive effect in silicon is primarily due to its insulator (SOI) technology [29] by Fraga et al. atomic level. As stress is applied, the average 2011. Later Haisheng San, Zijun Song, Xiang effective mass of the silicon carrier will either Wang, Yanlizhao, and Tuxi Y. U, proposed that increases or decreases (depending on the the silicon piezoresistive pressure sensor is a orientation of the crystallographic, direction of the mature technology in industry, but when the stress, and the direction of the current flow). This pressure sensors are operated in extremely harsh type of change alters the silicon carrier mobility environment, such as vibration, shock and and hence it results in the change in its resistivity. environment conditions with humidity, When piezoresistive element are placed in the alkalescency or acidity, electrostatic particles and Wheatstone bridge configuration and it is attached so on, its requirement in terms of reliability and to the pressure-sensitive diaphragm, a resistance stability is more rigorous than that of many change in the material is converted in to an output advanced applications so for these application we voltage which is proportional to the applied have to choose a SOI rather than silicon [30]. pressure as shown in the Fig.1.

III. PIEZORESISTIVE PRESSURE SENSING MECHANISM Piezoresistive, capacitive, optical, resonance, acoustic transduction principle used in the contemporary work within the progress of the micro machined pressure sensor modelling, design and fabrication used to be reviewed in [31]. Among these pressure sensor transduction principle, piezoresistive and capacitive transduction mechanisms have been widely adopted in various Fig.1. Conventional pressure sensor model fields. Many commercialized MEMS pressure sensor [32-36] uses a piezoresistive transduction mechanism in order to shows the pressure change in the resistance. Most researchers preferred piezoresistive technique, because the properties of silicon material have been well established and the facilities of current silicon foundry can be utilized for batch fabrication. And also piezoresistive pressure sensor has excessive high gauge factor but it has 0.27% per °C of temperature coefficient of Piezoresistivity (TCP). The design of piezoresistive pressure sensor consists of piezoresistive element Fig.2. Wheatstone bridge circuit. placed on a top of the diaphragm. Placement of piezoresistive element on the square diaphragm is Fig.2. shows the Wheatstone bridge very important design consideration to achieve the circuit, a Wheatstone bridge consists of a four required sensitivity. The optimal location to place piezoresistive material labeled as R1, R2, R3 and R4 the piezoresistive material would be in the region respectively. The resistance [R] of a piezoresistive of high stress on the diaphragm. Then these material is given by 푳 resistors are connected in the form of Whetstone's R= ρ (1) 푨 bridge [1, 37]. The application of pressure beneath Where ρ is the resistivity of a piezoresistor, L is the the sensor causes a deflection of the membrane and length of a piezoresistor; A is the area of a this causes a change in resistance of the piezoresistor. Wheatstone bridge is mounted on the piezoresistive elements. As a result, the calculation diaphragm. When the pressure is applied to the of stress distribution and deflection in accordance diaphragm, the diaphragm experiences the sheer with the applied pressure becomes pivotal. stress due to which the diaphragm deforms in the These forms of piezoresistive based direction of pressure imposed. Due to the transducers depend on the piezoresistive effect deformation of the diaphragm, the piezoresistors which occurs when the change in electrical mounted on the diaphragm in a Wheatstone bridge resistance of a material in response to the format stretches. As the piezoresistors stretches, the

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length increases while the area decreases. From ∆R/R = 훑풍훔풍 + 흅풕흈풕 (2) equation (1), if length increases and area decreases, Where 휎푙 is the longitudinal stress parallel to the there will be incremental change in the resistance current direction in the internal of resistance of a piezoresistors and effectively decreases the 2 (N/푚 ), 휎푡 is the transverse stress perpendicular to output voltage. 2 the current direction (N/푚 ), π푙 is the longitudinal piezoresistive coefficient of silicon (푚2/푁), the IV. MATERIALS OF PIEZORESISTIVE same direction as the longitudinal stress, π푡 is the PRESSURE SENSOR transverse piezoresistive coefficient of silicon In the above discussion it is clear that (푚2/푁), the same direction as the transverse stress. depending on the application we have to use a Table 3 shows the piezoresistive coefficient for different piezoresistive material for the model, like <100> silicon wafer. silicon (Si), silicon on insulator (SOI), silicon on sapphire (SOS), silicon carbide (SiC), steel, carbon Table 3 Piezoresistive coefficients of silicon nano tubes (CNT) and diamond. However the principle remains same as the piezoresistive Sl. Wafer π푙 π푡 Orientation mechanism of pressure sensing. The material used No type to design the diaphragm on which the 1. P-type -31.6 -17.16 <110> 2. N-type 71.8 -66.3 <110> piezoresistive materials are placed, plays on very

important role in deciding the application of a pressure sensor. Table 1 and 2lists the properties of V. PERFORMANCE PARAMETERS various diaphragm and piezoresistive material When the pressure is applied on the diaphragm, it respectively. tends to get deformed, having a maximum

displacement at the centre of the diaphragm. The

Table 1 Properties of various diaphragm materials value of displacement decreases near the fixed ends of the diaphragm. The quantity of displacement is Sl. Materials Density Young’s Poisson’ measured at the centre of the diaphragm [40] using No Modulus s ratio 1. Silicon di oxide 2270 70 0.17 the following equation ퟎ.ퟎퟎퟏퟐퟔ푷푳ퟒ 2. Poly Silicon 2320 169 0.22 X = (3) 3. Steel AISI 4340 7850 205 0.28 푫 Where P is the Pressure applied on the diaphragm, 4. Al203 3970 393 0.27 5. Si3N4 3310 317 0.23 L is the Length of the diaphragm, and D is the 6. Germanium 5323 103 0.26 Bending rigidity of the diaphragm material and is 7. Al 2700 70 0.25 given as 8. Cu 8960 120 0.34 푬풕ퟑ D = (4) ퟏퟐ(ퟏ−풗ퟐ) Table 2 Properties of various Where E is the Young’s Modulus of diaphragm piezoresistivematerials material, t is the thickness of the diaphragm, and v is the Poisson’s ratio of the diaphragm material. Sl. Materials Density Young’s Poisson’s The amount of sheer stress experienced at the mid- No Modulus ratio 1. Single 2270 70 0.17 point of the diaphragm [41] is given as crystalline Si (n, 푳 2 ρ = ( ) (5) p type) 풕 2. Carbon 1600 1000 0.2 It can be seen from (3) and (5) is that, increase in Nanotubes the pressure applied on the diaphragm, increases 3. Diamond 3.5 10.35 --- the sheer stress at the mid-point of the diaphragm, 4. SIC 3.21 476 0.19 also increases the displacement or deformation of 5. Silicon 2330 160 0.22 6. SOS 3.97 250-400 0.29 the diaphragm. The displacement of the diaphragm 7. Polycrystalline 2330 160 0.23 also depends on the dimensions of the diaphragm Si as well as the stiffness property (Young’s modulus) of the diaphragm material. When the pressure is In the piezoresistive pressure sensor applied on the diaphragm with four blocks as output signal is from the Wheatstone bridge. The piezoresistor, the stress induced in the diaphragm resistance of the bridge is distributed in four change the resistance of piezoresistor due to directions. The output signal Vout is Vin∆R/R. Vout piezoresistive effect. The change in the resistance is the output voltage (V), Vin is the input signal of the piezoresistor is denoted by ΔR. Due to the voltage (V), ∆R is the change in resistance (KΩ), deformation of the diaphragm in the direction of and R is the initialvalue of the resistance (KΩ). The pressure applied, it is said that the length of the amount of change in voltage sensitivity of resistors piezoresistor increases which in turn increases the is [39]. resistance of the piezoresistive material (using

www.ijera.com 26|P a g e Shwetha Meti et.al. Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 4, (Part - 1) April 2016, pp.23-31 equation 1). Thus it can be concluded that, as the relative change in the output voltage per unit of pressure increases, the resistance of the applied pressure [43]. The sensitivity of the piezoresistor will also increases linearly.The next piezoresistive pressure sensor is given by. ퟏ ∆푽 parameter is the output voltage across the S= (9) Wheatstone bridge. The output voltage of the 푽풊풏 ∆푷 Wheatstone bridge depends on the input voltage Where S is the sensitivity of the pressure sensor, applied to the bridge circuit and also the resistance ΔV is the change in the output voltage, and ΔP is values of all the four piezoresistive materials. the change in the pressure applied. The output Hence, as the resistance of the piezoresistive voltage of the pressure sensor without any pressure materials changes due to the applied pressure, the being applied is called an offset voltage. This is due output voltage of the Wheatstone bridge also to mainly two reasons. The first one is due to some varies. The output voltage [Vout] across the residual stress on the membrane. And the second Wheatstone bridge circuit is given by, one, which is main reason, is variability in the four 푹ퟐ푹ퟑ−푹ퟏ푹ퟒ resistors. While the resistors are processed at the V = [ ] V (6) out (푹ퟏ+푹ퟐ)(푹ퟑ+푹ퟒ) in same time, there are some variations. The offset Where Vin is the Input voltage applied to voltage can be compensated by connecting external Wheatstone bridgefrom (6), when R2R3 = R1R4, resistors. It can be compensated using Vout= 0. This means that the bridge is in the compensating resistors along with electronics. balanced condition and theoretically no pressure is applied onto the diaphragm. When there is no VI. DESIGN CONSIDERATION pressure on the diaphragm, the resistance values 6.1. Fracture Stress: of all the piezoresistive elements will be Fracture stress is a property which theoretically identical, hence Vout = 0. But describes the ability of a material containing a practically it may be difficult to fabricate the crack to resist fracture, and is one of the most piezoresistive elements of equal resistances, due important properties of any material for many to which the output voltage may not be zero when design applications. The linear-elastic fracture no pressure is applied. The relation of electric stress of a material is determined from the stress field in the vicinity of surface of the diaphragm intensity factor at which a thin crack in the material with applied stress is given by (7). begins to grow. It is denote (σfracture) E = ρ J + ρρ J (7) Where ρ is the resistivity of piezoresistors, J is 6.2. Yield Strength: the current in piezoresistors, and Δρ is the A yield strength or yield point is the induced change in resistivity. This is given by the material property defined as the stress at which a equation material begins to deform plastically. Prior to the ρρ = ρ. ρ yield point the material will deform elastically and Where π is the piezoresistance tensor and γ is the will return to its original shape when the applied shear stress given by (5).The performance of any stress is removed. Once the yield point is passed, model can be estimated based on the sensitivity some fraction of the deformation will be permanent of the sensor to the pressure applied and the and non-reversible.

gauge factor. For the system to be better, it should 6.3. Burst Pressure: be highly sensitive. In other words, there should Another important design consideration of be large decrease in the output voltage and large a piezoresistive pressure sensor is a burst pressure. increment in the resistance of piezoresistive We know that as the applied pressure on the element due to a small increase in the pressure diaphragm increases, the stress on the diaphragm applied to call a device as highly sensitive. Gauge increases correspondingly. As a result, when the factor is another parameter which determines the maximum stress on any portion of the diaphragm performance of the piezoresistive pressure sensor exceeds the yield strength of the diaphragm [42]. The Gauge factor of the pressure sensor is material, the diaphragm will burst. While this burst the change in resistance to the amount of pressure governs the maximum operating pressure volumetric strain acting on it. It is given by of a pressure sensor, the linearity of operation ∆푹 G = (8) determines the maximum pressure up to which the 푹휺 Where ε is the Strain of the pressure sensor sensor can be used within the limits of the specified accuracy. The burst pressure is decided by a The Gauge factor value should be large number of factors including diaphragm shape, (in the range of 500 to 1000) to indicate the better thickness, lateral dimensions, ruptures stress of the performance of the pressure sensor.The material and diaphragm surface roughness and is sensitivity of the pressure sensor is defined as the given by [44].

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ퟑ.ퟒ푭 풉ퟐ silicon wafer and a membrane has been formed by 푷 = 푴풂풙 (10) 풃 푨(ퟏ−풗ퟐ) an anisotropic etching using a KOH etch stop, in Where 퐹푀푎푥 is theFacture stress, h is the the <111> plane. Due to the nature of this etch; the Diaphragm thickness, 푣is the Poisson's ratio, A is sides of the membrane are oriented along <110> the Diaphragm area. direction.

6.4. Diaphragm dimension: As the stress on the piezoresistors is due to the stress on the diaphragm, it is important to choose the thickness and size of the diaphragm carefully in order to obtain the best output characteristics from the sensor. Pressure sensors with thinner diaphragms give better sensitivity whereas thicker diaphragm gives better linearity. Usually, the diaphragm in a pressure sensor is modified as a square diaphragm with all the edges Fig.3. Fabrication of the piezoresistive pressure clamped. A diaphragm can be considered as a thin sensor diaphragm, if the ratio of thickness to the length of diaphragm is less than 1/20, [44]. The small A cross sectional view of fabrication of a pure deflection theory for bending of thin plates assumes silicon based piezoresistive pressure sensors using that the deflection of midpoint of surface of the a standard silicon IC process is shown in the Fig.4. diaphragm must be small compared to the thickness The process of patterning the thin uniform layer of of the plate and the maximum deflection must be silicon substrate on the wafer surface. The pure less than 1/5th of the thickness of the diaphragm silicon is hardened by baking and then selectively [45]. removed by projection of light through a reticle

containing mask information. To form the 6.5. Temperature Coefficient diaphragm selectively removes unwanted material ofResistance(TCR): from the surface of the wafer using wet-etching The change in the resistance of the technique. In oxidation process wet oxidation material per degree Celsius change of temperature molecule convert silicon on the top the wafer to is known as the temperature coefficient of silicon dioxide. After the deposition of silicon resistance. A positive coefficient of the material dioxide layer piezoresistors are placed on the means that its resistance increases with increases in diaphragm by diffusing the P-type silicon to form the temperature (Pure metal typically have a bridge between the piezoresistors. positive temperature coefficient of resistance). A negative coefficient of the material means that its resistance decreases with an increases in the temperature (Semiconductor materials like carbon, silicon, germanium typically have a negative temperature coefficient of resistance). The equation for the TCR is given by, R= Rref[1+ρ (T-Tref)] (11) Where α is the temperature coefficient of resistance, R is the resistance of the material at temperature T, Rref is the reference resistance, T is the temperature in degree Celsius, and Tref is the reference temperature.

VII. FABRICATION METHODOLOGY Many fabrication methods have been investigated to date. They all aim at a thin Fig.4. Cross sectional view of fabrication monocrystalline silicon film on top of an insulator ofpiezoresistive pressure sensor

with defect densities as low as in bulk material. The best compatibility with standard silicon processing VIII. CONCLUSION techniques can be attained with sandwich Research activity in the areas related to the structures. A typical fabrication of the piezoresistive pressure sensor is very broad and it piezoresistive pressure sensor is shown in Fig.3. It has made a phenomenal growth. In this paper, an is made up of <100> crystal orientation of the

www.ijera.com 28|P a g e Shwetha Meti et.al. Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 4, (Part - 1) April 2016, pp.23-31 attempt has been made to provide a review on Diaphragm”,Microelectronic Engineering piezoresistive based pressure sensors, their various 85, 1054–1058 (2008). mechanisms, materials used to design the [9]. S. Park, B. S. Kang, D. W. Lee, and Y. S. piezoresistive pressure sensor, different fabrication Choi, “Single Carbon Fiber as a Sensing process; performance parameters for the Element in Pressure Sensors”, Appl. piezoresistive pressure sensors are discussed. The Phys. Lett.89,223516 (2006). piezoresistive pressure sensor based on Wheatstone [10]. M. Narayanaswamy, R. Joseph Daniel, K. bridge circuit is widely used by many reported Sumangala, C. Antony Jeyasehar, works. The exceptional properties, which allow “Computer aided modeling and piezoresistive pressure sensors to be used in diaphragm design approach for high sensors, has also been reviewed. MEMS pressure sensitivity Silicon-on-Insulator pressure sensor based on piezoresistive transduction sensors”, Measurement 44, 1924–1936, mechanism has lot of scope due to its high (2011). sensitivity, stability and high temperature. [11]. Onuma Y, Sekiya K, "Piezoresistive Properties of Polycrystalline Thin Films", REFERENCES Jpn. J. Appl. Phys. 1974, 11, 420-421. [1]. C.S. Smith, "Piezoresistance effect in [12]. Jaffe, J M Monolithic, "polycrystalline Germanium and Silicon", Physical silicon pressure transducer", IEEE Trans. Review, Vol.94, 1954, pp.42-49. Electron. Dev. 1983, ED-30, 420-421. [2]. Pfann, W.G. and Thurston, R.N, [13]. Luder E, "Polycrystalline silicon-based “Semiconducting stress transducers sensors", Sens. Actuat. 1986, 10, 9-23. utilizing the transverse and shear [14]. Gridchin, V ALubimsky, V M Sarina, piezoresistance effects”, Journal of "Piezoresistive properties of polysilicon Applied Physics, Vol. 32, No. 10, (1961). films", Sens. Actuat. A1995, 49, 67-72. [3]. Y. Kanda, “A graphical representation of [15]. Le Berre, M Kleimann, P Semmache, B the piezoresistance coefficients in Barbier, D Pinard, "Electrical and Silicon”, IEEE Transaction on Electron piezoresistive characterization of boron- Devices, vol. 29, No. 1, pp. 64–70, (1982). doped LPCVD polycrystalline silicon [4]. J.R. Mallon, F. Pourahmadi, K. Petersen, under rapid thermal annealing", Sens. Barth T. Vermeulen and Brezek J, “Low Actuat. A1996, 54, 700-703. Pressure Sensors employing bossed [16]. French P J, Evens A G R, diaphragms and precision etch stopping”, "Piezoresistance in polysilicon and its Sensors and Actuators’ Vol. A21–A23, applications to strain gauges", Solid-State 89–95, (1990). Electron. 1989, 32, 1-10. [5]. Roy Chaudhuri, V. Natarajan, P. [17]. Mikoshiba H, "Stress-sensitive properties Chatterjee, S. Gangopadhyay, of silicon-gate MOS devices", Solid-State Sreeramamurthy and H. Saha, “Design of Electron. 1981, 24, 221-232. a High Performance MEMS Pressure [18]. Iijima S, "Helical microtubules of Sensor Array with Signal Conditioning graphitic carbon", Nature1991, 354, 56– Unit for Oceanographic Applications”, 58. Sensors & Transducers Journal, Vol. 98, [19]. D S Bethune, C H Kiang, M S de Vries, Issue 11, pp. 83-95, (2008). G Gorman, R Savoy, J Vazquez, and R [6]. K. Sivakumar, N. Dasgupta, K.N. Bhat, Beyers, Nature 363, 305, 1993. “Sensitivity enhancement of [20]. A Thess, R Lee, P Nikolaev, H. J Dai, P polysiliconpiezo-resistive pressure sensors Petit, J Robert, C. H. Xu, Y H. Lee, S G with phosphorous diffused resistors”, Kim, A G Rinzler , D. T. Colbert, G E Journal of Physics, Conference Series 34, Scuseria, D Tomanek, J E. Fischer, R. E. 216–221, (2006). Smalley, Science 273, 483, 1996. [7]. Carmen K. M. Fung, Maggie Q. H. Zhang, [21]. M J Yacaman, M M Yoshida, L Rendon, J Zaili Dong and Wen J. Li, “Fabrication of G Santiesteban, Applied Physics Letter, CNT-Based MEMS Piezoresistive vol. 62, pp. 202, 1993. Pressure Sensors Using DEP Nano [22]. C. Liu, H. T. Cong, F. Li, P. H. Tan, H. M. assembly”, Proceedings of 5th IEEE Cheng, K. Lu, B. L. Zhou, Carbon, vol. Conference on Nanotechnology Nagoya, 37, pp. 1865, 1999. Japan (2005). [23]. H. Dai, in Topics in Applied Physics, [8]. Dong-Weon Lee, Young-Soo Choi, “A edited by M S Dresselhaus, G Novel Pressure Sensor with a PDMS Dresselhaus, P Avouris, Springer, New York (2001), vol. 80, pp. 29.

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Ms SHWETHA METI obtained her B.E degree in Electronics and Communication Engineering from the Basaveshwar Engineering College Bagalkot. Pursuing Master degree in Digital

Communication from the Basaveshwar EngineeringBasaveshwar College Bagalkot. Her area of interest includes MEMS, Piezoresistive pressure sensor, Capacitive pressure sensor, Digital signals processing.

Prof. KIRANKUMAR. B. BALAVALADcompleted his M.Techfrom VishweshwaryyaTechnological University, Belagavi, Karnataka, India in the year 2010. He is pursuing his Ph.D in the area of MEMS Piezoresistive Pressure Sensors. Presently he is serving as, Assistant Professor, Department of Electronics and Communication Engineering, Basaveshwar Engineering College, Bagalkot, Karnataka, India. He has published 20 papers in national and international conference and journals. His area of interest includes MEMS, Pressure sensors, Electro thermal actuators, Wireless networks, Statistical signal processing. Dr. B. G. Sheeparmatti hascompleted his Ph.D in the area of MEMS from Karnataka University Dharwad, Karnataka, India. He us currently serving as a professor in Electronics and Communication Engineering, department Basaveshwar Engineering College, Bagalkot, Karnataka, India. He has successfully completed 2RPS schemes approved by AICTE in the area of MEMS. He has setup a low cost MEMS fabrication lab at the department of Electronics and Communication Engineering. He has more than 60 national, international conference and journal papers to his credit. His area of interest includes MEMS, MEMS based actuators & sensors, Electromagnetic sensors and actuators, Embedded system etc.